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Date: Wed, 5 Dec 2018 19:16:05 +0000
From: Orivej Desh <orivej@....fr>
To: musl@...ts.openwall.com
Subject: sem_wait and EINTR

Hi,

musl differs from glibc in that it does not return from sem_wait() on EINTR.
This mail [1] explains that this is useful to safeguard the software that does
not check sem_wait() return code. However, since glibc does return EINTR, such
bugs in the open source software seem to be eventually noticed and fixed.

The musl behaviour has a disadvantage in that it makes sem_wait() difficult to
interrupt (and delays the return from sem_timedwait() until the timeout), which
is relied upon in particular by multithreaded fuse for breaking out of the
main thread waiting loop [2]. IMHO the fuse implementation is sensible, since it
looks better than the alternatives I could imagine, and I'm inclined to patch
musl like this [3] to meet its expectations.

Am I missing some implications? Would you reconsider returning from sem_wait()
on EINTR? Could you suggest a good fix for fuse that does not change musl?

[1] https://www.openwall.com/lists/musl/2018/02/24/3
[2] https://github.com/libfuse/libfuse/blob/fuse-3.3.0/lib/fuse_loop_mt.c#L332
[3] https://github.com/orivej/musl/commit/c4c38aaab4fc55c23669f7b81386b615609cc3e1

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